1. Field of the Invention
The present invention relates generally to cathode ray tube (CRT) bulbs. More specifically, the present invention relates to CRT bulbs having flat front panels, or faceplates, suitable for use with flat tensioned shadow masks.
2. Discussion of the Related Art
As is known the art of CRT construction, a CRT bulb is formed from a screen-bearing front glass panel affixed to a glass funnel section with cementitious material, normally a devitrifiable solder glass, or "frit". A CRT envelope is then formed by sealing an electron gun into a neck section of the bulb opposite the screen. The CRT envelope is then evacuated and sealed to become an operational, or finished, CRT.
Because the CRT is evacuated, atmospheric pressure produces stress on the CRT envelope. Thus the CRT must be designed so that the weakest portion of its envelope is able to withstand this atmospheric loading. The funnel-to-panel seal area, hereinafter "seal area", is one such weak area largely because the frit has a lower stress limit than the surrounding funnel and panel and because large bending moments are typically generated in this area due to panel deflection.
In the common CRT spherical faceplate, the faceplate, being analogous to an arch, has a shape which inherently resists the atmospheric load on the CRT. However, in the case of a tensioned mask CRT, which most commonly uses a flat front panel, the flat front panel shape does not inherently resist the atmospheric loading as well as a spherical panel.
In standard construction of the flat front panel CRT, the flat front panel is connected by frit to the funnel to form a rigid bulb without any significant stress placed on the front panel. Upon evacuation of the envelope, as the front panel deflects, large bending stresses will be placed on the frit and frontal seal land creating a potential failure point. In order to minimize the panel deflection and deflection-induced seal area stress, standard flat front panel CRT construction utilizes a thick glass for a stiffer front panel and a thick funnel seal land. The thick front panel will reduce deflection induced strains in the seal area and the thickened front seal land is incorporated into the funnel to further resist the remaining strain. However, in this arrangement, the thick front panel, being designed primarily for stiffness, is stressed well below its allowable limits and therefore represents wasted material in terms of envelope strength. While less susceptible to deflection, the thickened bulb members add weight and attendant material, and increased panel and/or funnel manufacturing and CRT processing time and shipping costs to the CRT.
Thus, it would be desirable to redistribute stress in an evacuated CRT bulb by reducing stress on the funnel seal land and frit while increasing stress in the panel to obtain good bulb strength while being able to utilize a thinner front panel or a narrower seal edge, or a combination of both. Conversely, a stronger CRT envelope may be made by utilizing bulb members of currently standard thicknesses.